fix(viewport): stabilize grid and grip clipping

Keep the grid on UCS XY, derive spacing from zoom, and clip perspective lines by screen density without dropping the near side.

src/app/helpers.rs

@@ -1,4 +1,3 @@
-use crate::ui::overlay::GridPlane;
 use acadrust::tables::Ucs;
 
 // ── Coordinate parsing ─────────────────────────────────────────────────────
@@ -160,22 +159,6 @@ pub(super) fn ucs_rotated_z(origin: glam::DVec3, angle_z: f32) -> Ucs {
     ucs
 }
 
-// ── Grid plane detection ───────────────────────────────────────────────────
-
-/// Choose the grid plane whose normal is most aligned with the camera view direction.
-pub(super) fn grid_plane_from_camera(pitch: f32, yaw: f32) -> GridPlane {
-    let fz = pitch.sin().abs();
-    let fy = (pitch.cos() * yaw.cos()).abs();
-    let fx = (pitch.cos() * yaw.sin()).abs();
-    if fz >= fy && fz >= fx {
-        GridPlane::Xy
-    } else if fy >= fx {
-        GridPlane::Xz
-    } else {
-        GridPlane::Yz
-    }
-}
-
 // ── Drawing constraint helpers ─────────────────────────────────────────────
 
 /// Constrain `pt` to the nearest 90° direction from `base`, in the active UCS

src/app/update/viewport.rs

@@ -962,15 +962,23 @@ impl OpenCADStudio {
             // content), so snap / hit-test / preview run exactly like the
             // main model view — no paper projection, tracks pan/zoom/twist.
             let cursor_world = self.cursor_model_point(i, &edit_cam, p, bounds);
-            let (view_rot, eye) = match &edit_cam {
-                Some(cam) => (cam.view_proj_rte(bounds), cam.eye()),
+            let (view_rot, eye, grid_spacing) = match &edit_cam {
+                Some(cam) => (
+                    cam.view_proj_rte(bounds),
+                    cam.eye(),
+                    crate::ui::overlay::compute_grid_step(cam.distance, cam.fov_y, bounds),
+                ),
                 None => {
                     let cam = self.tabs[i].scene.camera.borrow();
-                    (cam.view_proj_rte(bounds), cam.eye())
+                    (
+                        cam.view_proj_rte(bounds),
+                        cam.eye(),
+                        crate::ui::overlay::compute_grid_step(cam.distance, cam.fov_y, bounds),
+                    )
                 }
             };
             // Sync grid-snap spacing to the adaptive spacing of the visible grid.
-            self.snapper.grid_spacing = crate::ui::overlay::compute_grid_step(view_rot, bounds);
+            self.snapper.grid_spacing = grid_spacing;
             // Cursor and wires are model-space; the snap result is model.
             let snap_cursor = cursor_world;
 
@@ -1590,11 +1598,19 @@ impl OpenCADStudio {
         // Object/grid snap, same path as an entity grip or command drag: the
         // dragged UCS point sticks to endpoints/midpoints/grid under the cursor,
         // and the snap marker is published via `snap_result`.
-        let (view_rot, eye) = match &edit_cam {
-            Some(cam) => (cam.view_proj_rte(bounds), cam.eye()),
+        let (view_rot, eye, grid_spacing) = match &edit_cam {
+            Some(cam) => (
+                cam.view_proj_rte(bounds),
+                cam.eye(),
+                crate::ui::overlay::compute_grid_step(cam.distance, cam.fov_y, bounds),
+            ),
             None => {
                 let cam = self.tabs[i].scene.camera.borrow();
-                (cam.view_proj_rte(bounds), cam.eye())
+                (
+                    cam.view_proj_rte(bounds),
+                    cam.eye(),
+                    crate::ui::overlay::compute_grid_step(cam.distance, cam.fov_y, bounds),
+                )
             }
         };
         let all_wires = if let (Some(_), Some(h)) = (&edit_cam, self.tabs[i].scene.active_viewport)
@@ -1613,7 +1629,7 @@ impl OpenCADStudio {
             bounds,
             self.snapper.osnap_radius_px,
         );
-        self.snapper.grid_spacing = crate::ui::overlay::compute_grid_step(view_rot, bounds);
+        self.snapper.grid_spacing = grid_spacing;
         // No rubber-band origin (perp/extension feet don't apply to a free drag).
         self.snapper.from_point = None;
         let (go, gr) = self.tabs[i].ucs_grid_basis();

src/app/view/mod.rs

@@ -1,6 +1,5 @@
 use super::document::DocumentTab;
 use super::document::DynComponent;
-use super::helpers::grid_plane_from_camera;
 use super::history::history_dropdown_labels;
 use super::{Message, OpenCADStudio};
 use crate::scene::pick::grip::{grips_to_screen, grips_to_screen_paper, grips_to_screen_rte};
@@ -228,12 +227,15 @@ impl OpenCADStudio {
                     } else {
                         model_basis
                     };
-                    let plane = grid_plane_from_camera(cam.pitch, cam.yaw);
                     crate::ui::overlay::GridParams {
                         view_rot: cam.view_proj_rte(bounds),
                         eye: cam.eye(),
                         bounds,
-                        plane,
+                        step: crate::ui::overlay::compute_grid_step(
+                            cam.distance,
+                            cam.fov_y,
+                            bounds,
+                        ),
                         origin,
                         axes,
                     }
@@ -326,6 +328,17 @@ impl OpenCADStudio {
                 } else {
                     vec![]
                 };
+            let grip_clip = if grips.is_empty() {
+                None
+            } else {
+                let (vw, vh) = tab.scene.selection.borrow().vp_size;
+                Some(
+                    tab.scene
+                        .viewport_edit_frame((vw, vh))
+                        .map(|(_, bounds)| bounds)
+                        .unwrap_or_else(|| tab.scene.active_model_tile_bounds(vw, vh)),
+                )
+            };
 
             let (vw, vh) = tab.scene.selection.borrow().vp_size;
             // Active tile rectangle (canvas-offset included) so grid / UCS
@@ -508,6 +521,7 @@ impl OpenCADStudio {
                 snap_ext_base,
                 snap_ext_base2,
                 grips,
+                grip_clip,
                 ucs_icons,
                 ost_points,
                 otrack_line,